Container assembly and method for humidity control

ABSTRACT

A container assembly has a material storage container defining a sealed chamber therein. A quantity of moisture-sensitive material is disposed in the chamber. The moisture-sensitive material has a desired range of moisture content. A hydrated humidity control substance is also disposed within the chamber, and the humidity control substance is in humidity-transferable communication with the chamber. The humidity control substance regulates a relative humidity within the chamber in order to maintain a moisture content of the moisture-sensitive material within the desired range of moisture content.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Application No.60/640,558, filed Dec. 30, 2004 and U.S. Provisional Application No.60/640,975 filed Jan. 3, 2005.

BACKGROUND OF THE INVENTION

The present invention relates to a container and method for retaining amoisture-sensitive material. More specifically, the present inventionrelates to a container that has a moisture-sensitive material and ahumidity control substance, where the humidity control substanceregulates a relative humidity within a chamber of the container in orderto help the moisture-sensitive material maintain a desired range ofmoisture content.

Moisture-sensitive materials, such as pharmaceutical products, are oftenstored in hermetically and waterproof resealable containers. When openedfor access to those materials, however, there may be an exchange ofmoisture between the air inside the container and the air outside thecontainer. There may also be an exchange of moisture between the airinside the container and the air outside the container if there is anair leak in the container. The exchange of moisture may adversely affectthe properties of the moisture-sensitive material stored in thecontainer. The quality of moisture-sensitive material may be affected ifthe moisture level (also known as the “humidity level”) of the airinside the container falls below or rises above a desired level, in partbecause the moisture content of the moisture-sensitive material maychange. For this and other reasons, many manufacturers place anoff-the-shelf humidity control substance in the container to act as adesiccant and adsorb any excess moisture from the air inside thecontainer.

The desiccant may be any material that adsorbs moisture from the air,such as, but not limited to wood, cotton, bentonite clay, silica gel,montmorillonite clay, molecular sieve, calcium oxide, calcium sulfate,glycerol, sorbitol, sodium PCA, or propylene glycol. The desiccant maybe used to help keep the air inside the container at or below a desiredmoisture level by removing excess moisture from the air inside thecontainer.

The desiccant may be placed directly in a chamber of a material storagecontainer so that there is nothing separating the desiccant substancefrom the moisture-sensitive material. However, the desiccant is oftenpackaged in a container (“inner container” or “canister”) that has holesin it or a membrane designed to allow moisture into or out of the innercontainer and keep the desiccant (often in particle form) from leakingout of the inner container. The inner container may be formed of a rigidor non-rigid material. The inner container is usually placed inside achamber of the material storage container, in order for the desiccant tobe in humidity transferable communication with the chamber (and hence,the moisture-sensitive materials stored therein).

Off-the-shelf inner containers having a desiccant to adsorb any excessmoisture from the air inside the chamber of the material storagecontainer have been used. An “off-the-shelf” inner container being aninner container containing a preset amount of desiccant, where thedesiccant has a preset moisture content. When an off-the-shelf innercontainer is used, the manufacturer or bottler of the moisture-sensitivematerial has little control over the moisture level inside the chamberof the material storage container, and the manufacturer or bottler canonly maintain a generally dry environment. This may be undesirable ifthe moisture-sensitive material needs to be stored at a specificmoisture level in order to maintain its quality and/or if themoisture-sensitive material is readily affected by a large change inmoisture level.

BRIEF SUMMARY OF THE INVENTION

The present invention is a container assembly for retaining amoisture-sensitive material. The container assembly has a containerdefining a sealed chamber. A humidity control substance is disposedwithin the chamber of the container and is in humidity-transferablecommunication with the chamber. The humidity control substance regulatesa relative humidity within the chamber of the container in order to helpthe moisture-sensitive material maintain a desired range of moisturecontent.

In one aspect, the present invention is a container assembly including acontainer defining a sealed chamber therein, a quantity ofmoisture-sensitive material for healthcare use disposed in the chamber,the moisture-sensitive material having a desired range of moisturecontent, and a hydrated humidity control substance disposed within thechamber. The humidity control substance is in humidity-transferablecommunication with the chamber and regulates a relative humidity withinthe chamber in order to maintain a moisture content of themoisture-sensitive material within the desired range of moisturecontent.

In another aspect, the present invention is a method for controlling arelative humidity inside a container for retaining a moisture-sensitivematerial for healthcare use. The method includes hydrating a humiditycontrol substance to a desired moisture content, introducing thehumidity control substance into a chamber of the container in a humiditycontrolled environment, introducing the moisture-sensitive material intothe chamber of the container in the humidity controlled environment, andsealing the container.

The above summary of the present invention is not intended to describeeach disclosed embodiment or every implementation of the presentinvention. The FIGURE and the detailed description that follow moreparticularly exemplify illustrative embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further explained with reference to FIG.1, which is a perspective view of an exemplary embodiment a containerassembly in accordance with the present invention.

While the above-identified FIGURE sets forth one embodiment of theinvention, other embodiments are also contemplated, as noted in thediscussion. In all cases, this disclosure presents the invention by wayof representation and not limitation. It should be understood thatnumerous other modifications and embodiments can be devised by thoseskilled in the art, which fall within the scope and spirit of theprinciples of the invention.

DETAILED DESCRIPTION

The present invention is a container assembly having a material storagecontainer for retaining a moisture-sensitive material, where a desiredmoisture level is controlled inside a chamber of the container by ahumidity control substance. The humidity control substance regulates themoisture level inside the chamber of the container (i.e., bufferschanges in moisture level) in order to maintain a moisture content ofthe moisture-sensitive material within a desired range of moisturecontent. The moisture-sensitive material may be any healthcare-relatedmaterial, including, but not limited to, pharmaceutical products,medical products and devices, or dental materials or products, such as,but not limited to one or more capsules containing a dental materialcomposition or dental materials, such as, but not limited to, glassionomers, resin modified glass ionomers, dental adhesives, orthodonticadhesives, cements, restoratives, coatings, varnishes, sealants, and/orcomposite crowns.

The moisture level or humidity level is often expressed in terms ofrelative humidity (“RH”). Relative humidity may be defined as the ratioof the water vapor density of the air to the saturation water vapordensity of the air, and is usually expressed in percent.

Many moisture-sensitive materials contain moisture, and thus have amoisture content. The moisture content is the weight of water in amaterial expressed as a percentage of its dry weight. If themoisture-sensitive material is hygroscopic, the moisture content maydiffer depending upon the temperature and/or the RH of the airsurrounding the moisture-sensitive material. If the temperature or theRH of the surrounding air changes, the moisture content of themoisture-sensitive material may change so that it will come intoequilibrium with the new condition of the surrounding air.

If the moisture content of the moisture-sensitive material falls below adesired level, the properties and quality of the moisture-sensitivematerial may be adversely affected. The present invention addresses theproblems that may arise with a change in moisture content of amoisture-sensitive material due to a change in RH of the air surroundingthe moisture-sensitive material when the moisture-sensitive material isstored in a material storage container of a container assembly. Thepresent invention allows storage of moisture-sensitive materials in amaterial storage container assembly that has a RH that remains within adesired range.

If there is an exchange of air between a material storage container andthe air surrounding the container due to air leakage or another reason,the RH inside a chamber of the material storage container may increaseor decrease, depending upon the RH of the air surrounding the container.For example, if the RH inside the chamber is lower than the RHsurrounding the container and there is an exchange of air, the RH insidethe chamber may increase. Similarly, if the RH inside the chamber ishigher than the RH surrounding the container and there is an exchange ofair, the RH inside the chamber may decrease. The amount of the increaseor decrease in RH inside the chamber of the container depends upon theamount of air that is exchanged. The increase or decrease in RH insidethe chamber of the container may adversely affect the quality andshelf-life of the moisture-sensitive material stored in the chamber ofthe container because the moisture-sensitive material within the chambermay gain or lose some moisture content in order to remain in equilibriumwith the RH of the air inside the chamber.

It may be preferred to store moisture-sensitive material (whether forshipping, storing, and/or during use), such as dental capsules 18 ofFIG. 1, in an environment having a stable RH in order to limit the gainor loss of moisture content of the moisture-sensitive material. In anexemplary embodiment of the present invention, a stable RH is defined asa humidity level that stays within 10% of the desired RH. However, astable humidity level may differ depending upon many variables,including the type of moisture-sensitive material that is to be storedin the container. A person skilled in the art may modify the desiredstable RH.

A humidity control substance may be used to regulate the RH of the airinside the chamber in order to address the problems that may beassociated with the possible gain or loss of moisture content of themoisture-sensitive material that arise with a change in RH of the airinside the chamber. The humidity control substance may be any materialthat adsorbs moisture from the air and/or any hygroscopic(“water-pulling”) material that promotes retention of moisture, such as,but not limited to, wood, cotton, bentonite clay, silica gel,montmorillonite clay, molecular sieve, calcium oxide, calcium sulfate,glycerol, sorbitol, sodium PCA, or propylene glycol. The humiditycontrol substance may be used to help the moisture-sensitive materialmaintain its moisture content by either adding or subtracting moistureto the air inside the container in order to maintain a stable RH. Whenthe humidity control substance subtracts moisture from the air insidethe container, it acts as a desiccant; when the humidity controlsubstance adds moisture to the air inside the container, it acts as ahumectant.

The humidity control substance buffers RH changes within a container ofa container assembly during shipping and storage of themoisture-sensitive material. In this way, the humidity control substancehelps the moisture-sensitive material retain its moisture content withina desired range of moisture content. By helping the moisture-sensitivematerial retain its moisture content, the humidity control substance mayhelp the moisture-sensitive material retain its properties as well asextend a shelf-life of the moisture-sensitive material, even if thecontainer is opened and closed numerous times. A preferred bufferingrange for the humidity control substance is a range between about 10% RHto about 100% RH. A buffering range for a humidity control substance isthe range of RH for which the humidity control substance can buffer RHchanges, either by releasing moisture into the air inside the containeror by adsorbing moisture from the air inside the container. Thebuffering range of a humidity control substance depends on the bufferingcapacity, M_(H), at different RH values, and most humidity controlsubstances have an “optimum” RH range in which the M_(H) value is high.In order to provide effective RH control (“buffering effect”), it ispreferred that the humidity control substance have a high M_(H) valueover the desired RH range for the particular moisture-sensitive materialbeing stored. It is preferred that a container assembly in accordancewith the present invention be used for storing moisture-sensitivematerials that should be stored at an RH between about 10% to about 100%RH. A more preferred buffering range is about 30% RH to about 75% RH. Amost preferred buffering range is about 30% RH to about 60% RH.

The amount of humidity control substance that should be used in thecontainer assembly may be calculated by first estimating a maximumexpected amount of potential moisture loss (or a value close to themaximum) that the humidity control substance needs to compensate for.The maximum expected amount of potential moisture loss is the maximumamount expected for the particular container in the conditions in whichthe container assembly is reasonably expected to be used. The amount ofpotential moisture loss (W_(WATER)) for the particular in the particularconditions is calculated as a function of the moisture concentration (ingrams per pound of dry air) at the minimum tolerated RH inside thecontainer (C_(INSIDE)), the moisture concentration (in grams per poundof dry air) at the RH of the air surrounding the container(C_(OUTSIDE)), and the time the container assembly is reasonablyexpected to be used to store the moisture-sensitive material (T).Moisture concentration is measured as a function of the absolutehumidity of the air being measured. Both C_(INSIDE) and C_(OUTSIDE)depend upon the temperature of the air inside and outside the container,respectively. Similarly, the minimum tolerated RH of the air inside thecontainer also depends upon the temperature inside the chamber of thecontainer because moisture level in the air is dependent on temperature.

The following formula may be used to calculate the potential moistureloss that the humidity control substance may need to compensate for:W _(WATER) =K(C _(INSIDE) −C _(OUTSIDE))×TK is the moisture transmission constant of a specific container, and forthe first exemplary embodiment, K is calculated as 8.2×10⁻⁶ (pound ofdry air/day). Those skilled in the art can calculate K for a containerthat is to be used in a particular container assembly. It may not bepossible to accurately calculate the moisture concentration of the airsurrounding the container (C_(OUTSIDE)) because the exact conditions inwhich the container will be shipped, stored, and/or used may not beknown. However, for purposes of estimating the maximum (or near maximum)potential moisture loss inside the chamber of the container, C_(OUTSIDE)may be estimated by estimating the RH and temperature of the air outsidethe container at which the moisture content is near the lowest possiblemoisture content at which the container will be shipping, stored, and/orused.

After the potential moisture loss of the air inside the chamber iscalculated, the amount of humidity control substance that should be usedcan be calculated using the following formula:W _(HCS)=(W _(WATER) /[M _(H)(RH _(START) −RH _(END))])*1000.

W_(HCS) is the quantity of the humidity control substance (e.g., silicagel) that should be used in order to help maintain a desired RH range inthe chamber of the container, W_(WATER) is the amount of potentialmoisture loss inside the chamber that was calculated using the formuladiscussed above, and M_(H), the buffering capacity of a humidity controlsubstance, which may differ depending upon the type of humidity controlsubstance used. Specifically, M_(H) is the average amount of water (ingrams) that is gained or lost by one kilogram (kg) of the humiditycontrol substance for each one percent change in RH. A M_(H) value mayalso depend upon the range of RH the humidity control substance isregulating. For example, a regular density silica gel has a higher M_(H)when it is buffering a RH range having a maximum RH at or below about60% RH. RH_(START) is the RH inside the chamber of the container whenthe moisture-sensitive material is first placed inside the chamber.RH_(END) is the minimum tolerated RH the moisture-sensitive material maybe stored at before its quality is affected.

Either before or after the amount of humidity control substance that isrequired is calculated and measured out, the humidity control substancemay be hydrated (or “conditioned”) to a desired moisture content. Thehumidity control substance may be hydrated prior to being introducedinto the chamber of the container. The proper moisture content of thehumidity control substance is usually a moisture content which willallow the humidity control substance to maintain a RH of the air insidethe chamber of the container within a range of desired RH, which isalso, typically, the approximate range of RH at which themoisture-sensitive material should be stored in order to maintain itsdesired range of moisture content. The desired moisture content of thehumidity control substance will differ depending upon the desired RHrange and the buffering capacity of the humidity control substance. Inthe present invention, the moisture content of the humidity controlsubstance may depend on the RH level at which it is hydrated becausedifferent humidity control substances may adsorb different quantities ofmoisture at the same RH level. If it is known that the containerassembly is going to be shipped, stored, and/or otherwise used in a dryenvironment, the humidity control substance should probably be hydratedto a moisture level that will provide near the top of the desired RHrange because it is likely that the container will lose more moisture tothe surrounding air than if the container were shipped, stored, and/orotherwise used in a more humid environment.

One method of hydrating the humidity control substance is by placing thehumidity control substance in a constant humidity environment, such as asealed room or oven, where the humidity of the environment is set withinthe desired RH range. The humidity control substance should be left inthe constant humidity environment long enough for the humidity controlsubstance to become sufficiently hydrated. After the humidity controlsubstance is removed from the constant humidity environment, itsmoisture content may be measured or tested to ensure the humiditycontrol substance has been sufficiently hydrated. The moisture contentof the humidity control substance is measured by placing the humiditycontrol substance in a sealed space with a measuring instrument, such asa hygrometer. If the humidity control substance is not sufficientlyhydrated, the hydrating process may be repeated; the humidity controlsubstance may be placed in the constant humidity environment again andretested until the humidity control substance has the correct moisturecontent. The resulting moisture content of the humidity controlsubstance will differ depending upon the type of humidity controlsubstance used because, as stated above, different humidity controlsubstances will adsorb different quantities of moisture at the same RHlevel.

If a hydrated humidity control substance has a moisture content thatprovides a higher than proper RH for the particular container assembly,the humidity control substance may be dried, such as by using an oven.If after the drying process, the humidity control substance has a finitemoisture content, i.e. it is not “bone dry”, it may still be considered“hydrated”. In the present invention, a “hydrated” humidity controlsubstance is any humidity control substance that has a moisture contentthat allows it to buffer a RH range between about 10% RH to about 100%RH.

For moisture-sensitive materials that should be stored at around 40%-60%RH, such as dental capsules 18 of FIG. 1, silica gel is a preferredhumidity control substance. The most optimum buffering range for silicagel is between 40-60% RH. That is, silica gel has relatively high M_(H)at a RH between about 40% to about 60%. Silica gel is a porous,granular, chemically inert, amorphous form of silicon dioxide, which iscapable of adsorbing and desorbing water vapor in order to reachequilibrium with the surrounding air. Furthermore, most silica gels havean infinite life in terms of the ability to adsorb or desorb moisture,and may be reconditioned and reused indefinitely. There are manydifferent types of silica gel that may be used in the present invention.Those skilled in the art may select a silica gel based upon the silicagel's buffering capacity, the type of container assembly, and/or thetype of moisture-sensitive material that is going to be stored in thecontainer assembly.

Different configurations of silica gel may be used for purposes ofregulating a RH in a container assembly. For example, loose silica gelmay be used in the container assembly, or the silica gel may becontained in an inner container, such as a flexible packet or a rigidcontainer, which is then introduced into a chamber of a container of thecontainer assembly. If loose silica gel is used, a membrane may be usedto isolate the loose silica gel from the moisture-sensitive materialstored in the bottle. A rigid container may be a tin or canister. Thedifferent configurations of silica gel may also apply to all humiditycontrol substances in accordance with the present invention. In thepresent invention, a preferred configuration of silica gel for use in acontainer assembly for retaining moisture-sensitive materials thatshould be stored at around 40%-60% RH is silica gel contained in acanister. However, any other configuration may also be used.

Fungal growth may also be a concern when storing moisture-sensitivematerials in a humid environment Fungi generally require at least60%-65% RH for growth. Thus, the container assembly of the presentinvention should not support fungal growth as long as the RH in thechamber of the container remains lower than about 60%.

FIG. 1 is a perspective view of an exemplary embodiment of a containerassembly in accordance with the present invention. Container assembly 10is formed of container 12, canister 14, and cap 16. Container assembly10 may be used for storing a healthcare-related moisture-sensitivematerial, such as, but not limited to a pharmaceutical product, medicalproduct, medical device, or dental product. Examples of dental productsthat may be used in accord with the present invention include one ormore capsules containing a dental material composition, glass ionomers,resin modified glass ionomers, dental adhesives, orthodontic adhesives,cements, restoratives, coatings, varnishes, sealants, and/or compositecrowns. More particularly, the moisture-sensitive material may be storedin chamber 13, which is defined by cap 16 and the bottom and side wallsof container 12. In the embodiment shown in FIG. 1, chamber 13 is sealedby cap 16.

Container 12 and canister 14 may be formed of any material that does notreact with the moisture-sensitive contents of chamber 13, such as, butnot limited to, a plastic material or a glass material. Container 12and/or canister 14 may also be formed of a transparent material (asshown for container 12 in FIG. 1). Container 12 and canister 14 may alsobe formed of the same material, but it is not required for the presentinvention. Although container 12 is shown to be formed in acylindrically-shaped bottle, container 12 may be formed in any othershape, such as, but not limited to, a square or rectangular box.

A plurality of dental capsules 18 are stored in chamber 13 of container12. An example of dental capsules 18 that may be stored in the chamberof the container of the present invention is 3M ESPE Z100 MP RestorativeSystem, available from 3M Company, St. Paul, Minn., which is sold asnylon capsules containing dental restorative filling material. Nyloncapsules containing dental restorative filling material should be storedat a RH within a range of about 40% RH to about 60% RH. Although FIG. 1shows a plurality of dental capsules 18 stored in container assembly 10,any type of healthcare-related moisture-sensitive material may be usedwith the present invention, including pharmaceutical products, medicalproducts, medical devices, and other dental products (or materials),such as, but not limited to, glass ionomers, resin modified glassionomers, dental adhesives, orthodontic adhesives, cements,restoratives, coatings, varnishes, sealants, and/or composite crowns. Ifa glass ionomer or resin modified glass ionomer is stored in container12, it is preferred that chamber 13 of container 12 have a RH in a rangeof about 70% to about 90%.

A humidity control substance may be stored in canister 14. Canister 14may also be known as an “inner container”. Canister 14 of FIG. 1 isformed in a cylindrical shape. However, canister 14 may be any shapeand/or size that minimizes interference with the transfer of dentalcapsules 18 into or out of chamber 13 of container 12. It may also bepreferred to size canister 14 such that it is not easily removable fromcontainer 12. In an alternate embodiment, canister 14 may be formed of aflexible material, such as in a pillow-shaped pouch.

The air inside chamber 13 may be set at a desired RH at the time themoisture-sensitive material is deposited inside chamber 13. As containerassembly 10 is used, the RH inside chamber 13 may change, depending uponmany factors, including how many times cap 16 is opened and closed, theamount of air that leaks through a joint defined by cap 16 and container12, and the RH of the air outside of container 12. Even before containerassembly 10 is opened by a consumer, the RH of the air inside chamber 13may change. For example, if a seal is formed under cap 16 (such as afoil layer) or over cap 16 after moisture-sensitive material is“bottled” inside container 12 (where the seal is to be broken or removedby the consumer when container assembly 10 reaches the consumer), somemoisture may still leak through the seal.

In general, if the RH of the air surrounding container 12 is not thesame as the RH inside chamber 13 and there is air leakage, moisture maytransfer between chamber 13 and the surrounding air. Not only may airtransfer through possible leaks in the joint between cap 16 andcontainer 12, air may also transfer when cap 16 is opened (throughself-sealing flip-top 17 or otherwise), which may cause the RH insidechamber 13 to increase or decrease beyond the desired RH range. Anincreased or decreased RH inside chamber 13 may compromise the qualityof dental capsules 18 contained in chamber 13. The humidity controlsubstance may be used to address an excess or insufficient moistureproblem by giving up moisture to a drier atmosphere and absorbingmoisture from a humid atmosphere. More specifically, the humiditycontrol substance inside canister 14 may be used to address an excessmoisture problem by adsorbing some or all of the excess moisture toregulate the RH inside chamber 13 within a desired range. That is, ifthe RH in chamber 13 of container 12 exceeds a certain level, thehumidity control substance will adsorb the excess moisture. Similarly,the humidity control substance may also release moisture into chamber 13if the RH inside chamber 13 falls below a desired RH range. In this way,the humidity control substance may be used to help dental capsules 18retain their moisture content by maintaining a desired range of RH inchamber 13. In this way, the humidity control substance buffers RHchanges inside chamber 13.

A plurality of openings 15 in canister 14 provide a channel for humiditytransferable communication between the humidity control substance andchamber 13. That is, openings 15 allow the humidity control substance toeither extract or input moisture into chamber 13 of container 12.Openings 15 may be shaped such that the humidity control substance(often in particle form) does not leak from canister 14, or anothermechanism may be provided to prevent such leakage, such as a permeablemembrane. It may be important to keep substantially all of the humiditycontrol substance sealed in canister 14, because if the humidity controlsubstance contacts dental capsules 18 (or other moisture-sensitivematerial), the quality of dental capsules 18 may be compromised. Thehumidity control substance contained in canister 14 helps to keep thedental capsules 18 fresher and may also extend a shelf-life of dentalcapsules 18, even if container 12 is opened and closed numerous times.The humidity control substance should be designed to maintain theenvironment inside container 12 at the desired moisture level for aslong as container assembly 10 is reasonably expected to be used to storethe dental capsules 18.

Cap 16 provides a selectively resealable opening for access to chamber13. Cap 16 may be formed of any material that does not react with themoisture-sensitive contents of chamber 13, such as, but not limited to,a plastic material or a glass material. Cap 16 does not necessarily haveto be formed of the same material as container 12. In one embodiment,cap 16 has a flip top 17 that is connected to main body 20 of cap 16 byflexible connection 22. Flexible connection 22 may be any connectionthat allows flip top 17 to be opened and closed a plurality of timeswithout breaking, such as, but not limited to, a living hinge. Flip top17 allows container 12 to be selectively resealed once it has beenopened. When flip top 17 is lifted (as shown in FIG. 1), opening 24 isexposed, and a consumer may extract dental capsules 18 contained inchamber 13 of container 12 through opening 24. Flip top 17 allows a userto easily access the contents of container 12 without removing cap 16.

Cap 16 may be attached to container 12 by any method known in the art.For example, cap 16 may be “popped” onto container 12 by an interferencefriction fit, or cap 16 may be a twist-on cap. Although FIG. 1 showscontainer assembly 10 having cap 16 with flip top 17, cap 16 may be anyresealable mechanism. For example, cap 16 may just twist on withouthaving a flip-top. However, a flip-top arrangement may reduce thepossibility of a consumer losing cap 16 because cap 16 does not have tobe removed in order to access the contents of container 12.

In the embodiment shown in FIG. 1, it is preferred that dental capsules18 containing a dental composite material be stored in a containerassembly having a RH range of about 30% RH to about 50% RH. Assuming oneor more 3M ESPE Z100 MP Restorative System capsules are stored incontainer 12, container 12 has a volume of about 60 cubic centimeters,the RH outside container 12 is 15% at 25° C., the minimum tolerated RHinside container 12 is 30% at 25° C., K for container 12 is 8.2×10⁻⁶(pound of dry air/day) and container 12 is reasonably expected to beused for 180 days, the potential moisture loss of container 12 thesilica gel contained in canister 14 may need to compensate for(W_(WATER)) in order to store dental capsules 18 such that dentalcapsules 18 retain a desired range of moisture content, is calculatedusing the formula discussed above(W_(WATER)=K(C_(INSIDE)−C_(OUTSIDE))×T):W _(WATER)=[(8.2×10⁻⁶)(41.9 grams/pound of dry air−20.9 grams/pound ofdry air)]×180 days=0.031 grams

Using the amount of potential moisture loss, the quantity of silica gelthat should be used in order to help maintain a desired RH range inchamber 13 of container 12 for can be calculated using the followingtable (which is also discussed above):W_(HCS)=(W_(WATER)/[M_(H)(RH_(START)−RH_(END))])*1000. For purposes ofthe calculation, RH_(START) is 50% RH, where RH_(START) is the RH insidechamber 13 of container 12 when dental capsules 18 are introduced intochamber 13, and RH_(END) is 30% RH, where RH_(END) is the minimumtolerated RH dental capsules 18 may be stored at before their quality isaffected.

The quantity of silica gel will differ depending upon M_(H), thebuffering capacity of the type of silica gel used. The following tableshows the minimum quantity of silica gel (which is dried beforehydration) needed for three different types of silica gel having threedifferent buffering capacities: TABLE 1 Quantity of Silica Gel Type ofSilica Gel M_(H) W_(HCS) (in grams) Type A 2.0 0.78 Type B 4.5 0.34 TypeC 8.7 0.178

Either before or after the amount of silica gel that is required ismeasured out, the silica gel may be hydrated if necessary. As discussedabove, the silica gel may be hydrated by placing the silica gel in aconstant humidity room set at a desired RH.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. A container assembly comprising: a container defining a sealed chamber therein; a quantity of moisture-sensitive material for healthcare use disposed in the chamber, wherein the moisture-sensitive material has a desired range of moisture content; and a hydrated humidity control substance, wherein the humidity control substance is disposed within the chamber and is in humidity-transferable communication with the chamber, and wherein the humidity control substance regulates a relative humidity within the chamber in order to maintain a moisture content of the moisture-sensitive material within the desired range of moisture content.
 2. The container assembly of claim 1, wherein the humidity control substance is a silica gel.
 3. The container assembly of claim 2, wherein the silica gel is a buffered silica gel.
 4. The container assembly of claim 1, wherein the humidity control substance has a preferred buffering range of between 10 percent to about 100 percent relative humidity.
 5. The container assembly of claim 4, wherein the humidity control substance has a preferred buffering range of between 30 percent to about 75 percent relative humidity.
 6. The container assembly of claim 4, wherein the humidity control substance has a preferred buffering range of between about 30 percent to about 60 percent relative humidity.
 7. The container assembly of claim 1, wherein the moisture-sensitive material is a dental material.
 8. The container assembly of claim 7, wherein the dental material is selected from a group consisting of glass ionomers, resin modified glass ionomers, dental adhesives, orthodontic adhesives, cements, restoratives, coatings, varnishes, sealants, and composite crowns.
 9. The container assembly of claim 7, wherein the moisture-sensitive material is one or more capsules, each capsule containing a dental composition therein.
 10. The container assembly of claim 1, wherein the container can be opened and is selectively resealable.
 11. The container assembly of claim 1 wherein the container has a single opening for access to the chamber therein, and wherein the container has a cap for resealably covering the opening.
 12. The container assembly of claim 11 wherein the cap is flexibly attached to the container.
 13. A method for controlling a relative humidity inside a container, where the container is for retaining a moisture-sensitive material for healthcare use, the method comprising: hydrating a humidity control substance to a desired moisture content; introducing the humidity control substance into a chamber of the container in a humidity controlled environment; introducing the moisture-sensitive material into the chamber of the container in the humidity controlled environment; and sealing the container.
 14. The method of claim 13, wherein the step of hydrating comprises: selecting a desired relative humidity of the chamber of the container as a function of the moisture-sensitive material to be stored in the chamber of the container; selecting a desired moisture content of the humidity control substance as a function of the desired relative humidity of the chamber of the container; placing the humidity control substance in a constant humidity environment, where the environment is set at the desired relative humidity; removing the humidity control substance from the constant humidity environment and placing the humidity control substance in a sealed space; and testing a moisture content of the humidity control substance to determine whether the humidity control substance has the desired moisture content.
 15. The method of claim 13 wherein, prior to introducing the humidity control substance into the chamber of the container, an amount of humidity control substance that should be used in the container is determined by estimating a potential moisture loss from the container. 